Draw-off devices, also called take-down devices, of this kind are known especially in warp knitting machine (U.S. Pat. Nos. 2,649,811, 2,760,362) and comprise at least one take-down roller, a drive source and a transmission connecting the take-down roller and the drive source. The transmission is or comprises a V-belt transmission which includes a V-belt pulley formed as a control pulley, with two conical flanges, of which at least one is mounted so as to be axially movable, in order to alter the effective diameter of the V-belt pulley, a V-shaped belt at least partially wrapping round the V-belt pulley and a device for adjusting the take-down tension, by means of which a displacement of the movable flange can be effected through alteration of the tension in the V-belt. Such draw-off devices serve for stepless adjustment of the winding-up speed of a winding-up roller, at the same time however to adjust for different tensions in the goods taken down. The V-belt pulley there consists of two immovable conical flanges, between which an axially movable further flange which is conical on both sides is arranged. Two adjacent V-shaped sections thereby result for reception of a V-shaped belt in each, which belts centre between the movable and an associated fixed flange. The effective diameter of each section thus depends on the instantaneous axial position of the movable flange. This position can be affected by a displacement radially relative to the running direction of the two V-belts or by tilting the V-belt pulley, since the tension of one V-belt is thereby momentarily increased and the tension of the other V-belt is momentarily reduced. The inequality thereby created automatically results in corresponding displacement of the movable flange and corresponding alteration of the effective diameters of the two sections of the V-belt pulley. Accordingly the relative speeds of circulation of the two V-belts alter and the transmission ratio of the V-belt drive or the overall drive including the same alters.
The described V-belt drive is comparatively complex and sensitive. It further requires the use of a tilting or shift mechanism for the V-belt or control pulley as well as the use of two V-belts to compensate for the shifting or like displacement of the axis of the V-belt pulley. Both of these are not always desirable. The cited disadvantages can it is true be partially avoided by use of another known V-belt drive (FR 915 696, DE 88 00 999 U1, DE 3 213 950 A1, DE 3 601 825 A1) but with this a manual change in the diameter of the V-belt pulley is necessary with the take-down mechanism at rest, which is likewise troublesome and in most cases undesirable.